# How do I read a power supply?

#### tuesday0180

##### Distinguished
I've been hearing that it isn't about how many watts I have, but what I have on the 12 rails. I don't know what that means.

I have a thermal take 600watt purepower.
It says I have

Does the 1 and 2 next to the 12v mean the rails? What's a real anyways?

Solution
A rail is just a term that we use for the different voltages that come out of the power supply each voltage is considered on its own rail. Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps for a 600watt power supply that is a little on the weak side for the 12 volt rail. However depending on your system the Average single Graphics card system that is more then enough to power your system.

#### saaiello

##### Splendid
A rail is just a term that we use for the different voltages that come out of the power supply each voltage is considered on its own rail. Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps for a 600watt power supply that is a little on the weak side for the 12 volt rail. However depending on your system the Average single Graphics card system that is more then enough to power your system.

#### enzo matrix

##### Splendid
Something not mentioned is why the +12V rails are important. These rails provide power for your CPU and the expansion slots (including a graphics card). These components draw the most power. I believe the ram runs on the +5V and I'm not sure about the others. Someone correct me if I am wrong.

#### tuesday0180

##### Distinguished
Hey thanks guys. I sort of understand now. I just need to pay attention to the 12v. I did get my thermaltake on discount. It was only like \$60.00 or so.

I'm concerned about my popwersupply when I upgrade though. I currently have a

E5200 2.5gig dual core with 4 gigs ddr2 ram, a dvd drive, GTX 260 graphics card and 2 hard drives.

I'm upgrading to maybe an AMD AM3 motherboard with a Phenom or Athlon x4 chip. Will my current 600watt 36amp power supply need to be replaced?

#### saaiello

##### Splendid
Yes it should be fine powering that system. You will only really need to upgrade if you go for a more powerful video card but you will be fine with your current setup and the future AM3 setup.

Good Luck

#### 4745454b

##### Titan
Moderator
Your power supply has 2 12v rails pushing 18 amps a peice so a combined total of 36 amps

Again, it doesn't work that way. It can work that way, but thats not how you determine the COMBINED 12V amperage. You need to find the statement like JSC did and then do the math. My delta sourced EA500W is my favorite example. Each rail is rated at 22A, but I don't have 44A of power on the 12V rail. I only have 34.

#### enzo matrix

##### Splendid

P=VI
Don't confuse units with the symbol.

264W on each rail (I=22A and V= 12V) does not mean it will allow a total draw of 528W
Here's a chart from OCZ:
http://www.ocztechnology.com/images/awards/mxsp_wattage_charts.jpg
Note that their 700W PSU has the same number of rails and the same amps per rail as their 600W, yet provides more power across both rails.

#### 4745454b

##### Titan
Moderator
Your missing the point. 18A on 12v1 + 18A on 12v2 != 36A. It might in some cases, but that's not the way you figure out how many amps the PSU can provide. You don't have to spell out the words, you can use the correct abbreviations.

Moderator

#### enzo matrix

##### Splendid

Excuse me? I did not visit wikipedia at all. This comes from my experience in computer engineering.

#### Starges

##### Distinguished
So how exactly do yu determine the total power on the 12v rail?

#### enzo matrix

##### Splendid

I've been trying to figure that out since I found out that it's not VI+VI. So far, all I can figure out is that you have to check with the manufacturer. If you look at the link I posted, both the 600W and 700W versions have the same amps on the +12V rails and the same number of rails but one supports 500W and the other 550W.

#### 4745454b

##### Titan
Moderator
The only way to know before you buy is to look at the label. The manufacturer has to list total power available on the 12V rail(s) combined. Usually written as "12v1 and 12v2 not to exceed 408W" or some other total output number. Do the math, you'll get your amperage. If they don't list it, you can perhaps find a review where they test it. Other then that, you really have no idea.

#### jsc

##### Champion

OK. RAM runs of the 3.3 volt rail. It uses a simplified version of the programmable power regulator that the CPU does. Measurements on my first Core2 system indicated that 2 GB of DDR2 RAM running at 2.1 volts pulled 6 amps or 20 watts of power.

I buy single rail Corsairs now.

But you could read the PSU label (see my two links above) and if the label doesn't tell you the total (like the first), don't buy the PSU.

I also have an Antec 650 watt TP3. It has 3 rails (allegedly), each max rated at 19 amps. The label also says that max 12 volt output is 624 watts (52 amps).

#### Starges

##### Distinguished
Why is it that some PSUs have lots of amperage (up to 30A) in the +3.3v rail and very little the +12v rail? Apart from RAM, what else does this rail (the +3.3v rail) provide power to? [:fixitbil:1]

#### jsc

##### Champion

Obsolete design , dressed up with modern cables.

SATA drives. 3.3 volts comes off the orange wires.

#### enzo matrix

##### Splendid

So they can say it's a 600W power supply when the +12V rails can only provide as much as a modern 300W.